1,720,969 research outputs found
An Efficient Reliability-based Design Approach to Reduce Rockfall Risk Below a Target Threshold
Full text linkRockfalls are expected to increase due to global warming and extreme events induced by climate change. An accurate quantification of the risk is fundamental for Administrations to predispose effective risk mitigation plans. Risk value should account for all the possible events that can occur in a specific time, i.e. for a magnitude (block volume) frequency relationship. Among structural protective measures, rockfall barriers are widely selected. Despite their design method has been almost defined, even not standardized, the widely adopted safety factors approach with fixed factors does not allow obtaining a specific probability of failure. Moreover, the event magnitude-frequency relationship is not accounted. A novel time- independent reliability-based approach has been recently conceived by the Authors, allowing obtaining the design values for a specific failure probability. The method accounts for all the possible events, integrating them in time with their probability. In this way, an increase of rockfall events can been accurately considered. The obtained barrier failure probability can be used to compute the risk reduction in a given time or, conversely, to define the maximum failure probability of a barrier that could be accepted
Optimization methods for the evaluation of the parameters of a rockfall fractal fragmentation model
No full textIn rockfall events, the falling blocks impacting the slope can experience fragmentation due to their kinetic energy. This process produces new blocks, smaller than the initial ones, moving along independent trajectories. As a result, the in situ block size distribution (related to the slope face of the source area) and the rockfall block size distribution (related to the deposit) differ. The present paper proposes and compares two optimization procedures for choosing the parameters of an iterative fractal fragmentation model based aimed at describing the rockfall fragmentation process on the base of source and deposit block distributions. To discuss the effectiveness of each approach, the two distributions are considered free of uncertainties. The influence of the number of iterations and optimization approach are discussed in terms of easiness of interpretation of the results
Reliability analysis and partial safety factors approach for rockfall protection structures
No full textThe design of rockfall protection structures must consider several variables, such as the energy and the height of the impacting block. Nevertheless, the statistical distributions of these variables do not follow a predefined law. Reliability analyses aim at finding how the random nature of the parameters describing a structure affects its performance and safety. In the geotechnical framework, generally, the limit states approach is adopted, accounting for the design values of both effects of actions and resistances. The present paper proposes a solution to a time-variant reliability problem to define the design values of the parameters for net fences design, i.e. velocity, mass and trajectory height of the impacting block, accounting for the spreading of their distributions and rockfall occurrence process. The proposed approach is incorporated into the semi-probabilistic design framework and the equivalent partial safety factors of the main variables and the corresponding characteristic values are discussed. The results highlights that the values of the partial safety factors are affected by the ratios between two relevant values of the right-tail of the distributions of height and velocity, i.e. the 99th and the 95th percentiles, and by the parameters of the statistical distribution of the blocks found at the foot of the cliff
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Towards a procedure to manage safety on construction sites of rockfall protective measures
No full textConstruction sites represent ones of the most dangerous workplaces, due to the huge number of hazards related to the performed activities that can cause discomfort, health diseases, and even death to workers. These issues might be even more amplified in construction sites of structures aiming at preventing or protecting against natural hazards. Among these lasts, rockfall represents one of the most unpredictable and dangerous. In these sites, the inherent added hazard is represented by the occurrence of the event against which the protection is required to be installed, i.e. the detachment of a rock block. As in the other situations, workers might be aware of the danger to which they are subjected and all the possible measures to mitigate the risk should be implemented. To address these issues and increase safety of workers, this paper proposes a quantitative risk assessment method to compute the probability of death of workers due to the occurrence of a rockfall event in the considered work duration. In addition, preliminary suggestions to improve safety of workers are delineated
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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